Generating parameter file for a metalloid

GROMACS version:2018
GROMACS modification: Yes/No
Hello all , I created the parameter files UNL.parm7 and UNL.rst7 for the metalloid in amber using leap script .Now I want to do simulation in the Gromacs engine using forcefield charm36.How can I use above two files in gromacs or add them in gromacs forcefield .
Thanks in advance